//
// MessagePack for Java
//
//    Licensed under the Apache License, Version 2.0 (the "License");
//    you may not use this file except in compliance with the License.
//    You may obtain a copy of the License at
//
//        http://www.apache.org/licenses/LICENSE-2.0
//
//    Unless required by applicable law or agreed to in writing, software
//    distributed under the License is distributed on an "AS IS" BASIS,
//    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
//    See the License for the specific language governing permissions and
//    limitations under the License.
//
package org.msgpack.core.buffer;

import sun.misc.Unsafe;

import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.nio.BufferOverflowException;
import java.nio.ByteBuffer;
import java.nio.ByteOrder;

import static org.msgpack.core.Preconditions.checkArgument;
import static org.msgpack.core.Preconditions.checkNotNull;

/**
 * MessageBuffer class is an abstraction of memory with fast methods to serialize and deserialize primitive values
 * to/from the memory. All MessageBuffer implementations ensure short/int/float/long/double values are written in
 * big-endian order.
 * <p>
 * Applications can allocate a new buffer using {@link #allocate(int)} method, or wrap an byte array or ByteBuffer
 * using {@link #wrap(byte[], int, int)} methods. {@link #wrap(ByteBuffer)} method supports both direct buffers and
 * array-backed buffers.
 * <p>
 * MessageBuffer class itself is optimized for little-endian CPU archtectures so that JVM (HotSpot) can take advantage
 * of the fastest JIT format which skips TypeProfile checking. To ensure this performance, applications must not import
 * unnecessary classes such as MessagePackBE. On big-endian CPU archtectures, it automatically uses a subclass that
 * includes TypeProfile overhead but still faster than stndard ByteBuffer class. On JVMs older than Java 7 and JVMs
 * without Unsafe API (such as Android), implementation falls back to an universal implementation that uses ByteBuffer
 * internally.
 */
public class MessageBuffer
{
    static final boolean isUniversalBuffer;
    static final Unsafe unsafe;

    /**
     * Reference to MessageBuffer Constructors
     */
    private static final Constructor<?> mbArrConstructor;
    private static final Constructor<?> mbBBConstructor;

    /**
     * The offset from the object memory header to its byte array data
     */
    static final int ARRAY_BYTE_BASE_OFFSET;

    private static final String UNIVERSAL_MESSAGE_BUFFER = "org.msgpack.core.buffer.MessageBufferU";
    private static final String BIGENDIAN_MESSAGE_BUFFER = "org.msgpack.core.buffer.MessageBufferBE";
    private static final String DEFAULT_MESSAGE_BUFFER = "org.msgpack.core.buffer.MessageBuffer";

    static {
        boolean useUniversalBuffer = false;
        Unsafe unsafeInstance = null;
        int arrayByteBaseOffset = 16;

        try {
            // Check java version
            String javaVersion = System.getProperty("java.specification.version", "");
            int dotPos = javaVersion.indexOf('.');
            boolean isJavaAtLeast7 = false;
            if (dotPos != -1) {
                try {
                    int major = Integer.parseInt(javaVersion.substring(0, dotPos));
                    int minor = Integer.parseInt(javaVersion.substring(dotPos + 1));
                    isJavaAtLeast7 = major > 1 || (major == 1 && minor >= 7);
                }
                catch (NumberFormatException e) {
                    e.printStackTrace(System.err);
                }
            }

            boolean hasUnsafe = false;
            try {
                hasUnsafe = Class.forName("sun.misc.Unsafe") != null;
            }
            catch (Exception e) {
            }

            // Detect android VM
            boolean isAndroid = System.getProperty("java.runtime.name", "").toLowerCase().contains("android");

            // Is Google App Engine?
            boolean isGAE = System.getProperty("com.google.appengine.runtime.version") != null;

            // For Java6, android and JVM that has no Unsafe class, use Universal MessageBuffer
            useUniversalBuffer =
                    Boolean.parseBoolean(System.getProperty("msgpack.universal-buffer", "false"))
                            || isAndroid
                            || isGAE
                            || !isJavaAtLeast7
                            || !hasUnsafe;

            if (!useUniversalBuffer) {
                // Fetch theUnsafe object for Oracle and OpenJDK
                Field field = Unsafe.class.getDeclaredField("theUnsafe");
                field.setAccessible(true);
                unsafeInstance = (Unsafe) field.get(null);
                if (unsafeInstance == null) {
                    throw new RuntimeException("Unsafe is unavailable");
                }
                arrayByteBaseOffset = unsafeInstance.arrayBaseOffset(byte[].class);
                int arrayByteIndexScale = unsafeInstance.arrayIndexScale(byte[].class);

                // Make sure the VM thinks bytes are only one byte wide
                if (arrayByteIndexScale != 1) {
                    throw new IllegalStateException("Byte array index scale must be 1, but is " + arrayByteIndexScale);
                }
            }
        }
        catch (Exception e) {
            e.printStackTrace(System.err);
            // Use MessageBufferU
            useUniversalBuffer = true;
        }
        finally {
            // Initialize the static fields
            unsafe = unsafeInstance;
            ARRAY_BYTE_BASE_OFFSET = arrayByteBaseOffset;

            // Switch MessageBuffer implementation according to the environment
            isUniversalBuffer = useUniversalBuffer;
            String bufferClsName;
            if (isUniversalBuffer) {
                bufferClsName = UNIVERSAL_MESSAGE_BUFFER;
            }
            else {
                // Check the endian of this CPU
                boolean isLittleEndian = ByteOrder.nativeOrder() == ByteOrder.LITTLE_ENDIAN;
                bufferClsName = isLittleEndian ? DEFAULT_MESSAGE_BUFFER : BIGENDIAN_MESSAGE_BUFFER;
            }

            try {
                // We need to use reflection here to find MessageBuffer implementation classes because
                // importing these classes creates TypeProfile and adds some overhead to method calls.

                // MessageBufferX (default, BE or U) class
                Class<?> bufferCls = Class.forName(bufferClsName);

                // MessageBufferX(byte[]) constructor
                Constructor<?> mbArrCstr = bufferCls.getDeclaredConstructor(byte[].class, int.class, int.class);
                mbArrCstr.setAccessible(true);
                mbArrConstructor = mbArrCstr;

                // MessageBufferX(ByteBuffer) constructor
                Constructor<?> mbBBCstr = bufferCls.getDeclaredConstructor(ByteBuffer.class);
                mbBBCstr.setAccessible(true);
                mbBBConstructor = mbBBCstr;
            }
            catch (Exception e) {
                e.printStackTrace(System.err);
                throw new RuntimeException(e); // No more fallback exists if MessageBuffer constructors are inaccessible
            }
        }
    }

    /**
     * Base object for resolving the relative address of the raw byte array.
     * If base == null, the address value is a raw memory address
     */
    protected final Object base;

    /**
     * Head address of the underlying memory. If base is null, the address is a direct memory address, and if not,
     * it is the relative address within an array object (base)
     */
    protected final long address;

    /**
     * Size of the underlying memory
     */
    protected final int size;

    /**
     * Reference is used to hold a reference to an object that holds the underlying memory so that it cannot be
     * released by the garbage collector.
     */
    protected final ByteBuffer reference;

    /**
     * Allocates a new MessageBuffer backed by a byte array.
     *
     * @throws IllegalArgumentException If the capacity is a negative integer
     *
     */
    public static MessageBuffer allocate(int size)
    {
        if (size < 0) {
            throw new IllegalArgumentException("size must not be negative");
        }
        return wrap(new byte[size]);
    }

    /**
     * Wraps a byte array into a MessageBuffer.
     *
     * The new MessageBuffer will be backed by the given byte array. Modifications to the new MessageBuffer will cause the byte array to be modified and vice versa.
     *
     * The new buffer's size will be array.length. hasArray() will return true.
     *
     * @param array the byte array that will gack this MessageBuffer
     * @return a new MessageBuffer that wraps the given byte array
     *
     */
    public static MessageBuffer wrap(byte[] array)
    {
        return newMessageBuffer(array, 0, array.length);
    }

    /**
     * Wraps a byte array into a MessageBuffer.
     *
     * The new MessageBuffer will be backed by the given byte array. Modifications to the new MessageBuffer will cause the byte array to be modified and vice versa.
     *
     * The new buffer's size will be length. hasArray() will return true.
     *
     * @param array the byte array that will gack this MessageBuffer
     * @param offset The offset of the subarray to be used; must be non-negative and no larger than array.length
     * @param length The length of the subarray to be used; must be non-negative and no larger than array.length - offset
     * @return a new MessageBuffer that wraps the given byte array
     *
     */
    public static MessageBuffer wrap(byte[] array, int offset, int length)
    {
        return newMessageBuffer(array, offset, length);
    }

    /**
     * Wraps a ByteBuffer into a MessageBuffer.
     *
     * The new MessageBuffer will be backed by the given byte buffer. Modifications to the new MessageBuffer will cause the byte buffer to be modified and vice versa. However, change of position, limit, or mark of given byte buffer doesn't affect MessageBuffer.
     *
     * The new buffer's size will be bb.remaining(). hasArray() will return the same result with bb.hasArray().
     *
     * @param bb the byte buffer that will gack this MessageBuffer
     * @throws IllegalArgumentException given byte buffer returns false both from hasArray() and isDirect()
     * @throws UnsupportedOperationException given byte buffer is a direct buffer and this platform doesn't support Unsafe API
     * @return a new MessageBuffer that wraps the given byte array
     *
     */
    public static MessageBuffer wrap(ByteBuffer bb)
    {
        return newMessageBuffer(bb);
    }

    /**
     * Creates a new MessageBuffer instance backed by a java heap array
     *
     * @param arr
     * @return
     */
    private static MessageBuffer newMessageBuffer(byte[] arr, int off, int len)
    {
        checkNotNull(arr);
        return newInstance(mbArrConstructor, arr, off, len);
    }

    /**
     * Creates a new MessageBuffer instance backed by ByteBuffer
     *
     * @param bb
     * @return
     */
    private static MessageBuffer newMessageBuffer(ByteBuffer bb)
    {
        checkNotNull(bb);
        return newInstance(mbBBConstructor, bb);
    }

    /**
     * Creates a new MessageBuffer instance
     *
     * @param constructor A MessageBuffer constructor
     * @return new MessageBuffer instance
     */
    private static MessageBuffer newInstance(Constructor<?> constructor, Object... args)
    {
        try {
            // We need to use reflection to create MessageBuffer instances in order to prevent TypeProfile generation for getInt method. TypeProfile will be
            // generated to resolve one of the method references when two or more classes overrides the method.
            return (MessageBuffer) constructor.newInstance(args);
        }
        catch (InstantiationException e) {
            // should never happen
            throw new IllegalStateException(e);
        }
        catch (IllegalAccessException e) {
            // should never happen unless security manager restricts this reflection
            throw new IllegalStateException(e);
        }
        catch (InvocationTargetException e) {
            if (e.getCause() instanceof RuntimeException) {
                // underlying constructor may throw RuntimeException
                throw (RuntimeException) e.getCause();
            }
            else if (e.getCause() instanceof Error) {
                throw (Error) e.getCause();
            }
            // should never happen
            throw new IllegalStateException(e.getCause());
        }
    }

    public static void releaseBuffer(MessageBuffer buffer)
    {
        if (isUniversalBuffer || buffer.hasArray()) {
            // We have nothing to do. Wait until the garbage-collector collects this array object
        }
        else if (DirectBufferAccess.isDirectByteBufferInstance(buffer.reference)) {
            DirectBufferAccess.clean(buffer.reference);
        }
        else {
            // Maybe cannot reach here
            unsafe.freeMemory(buffer.address);
        }
    }

    /**
     * Create a MessageBuffer instance from an java heap array
     *
     * @param arr
     * @param offset
     * @param length
     */
    MessageBuffer(byte[] arr, int offset, int length)
    {
        this.base = arr;  // non-null is already checked at newMessageBuffer
        this.address = ARRAY_BYTE_BASE_OFFSET + offset;
        this.size = length;
        this.reference = null;
    }

    /**
     * Create a MessageBuffer instance from a given ByteBuffer instance
     *
     * @param bb
     */
    MessageBuffer(ByteBuffer bb)
    {
        if (bb.isDirect()) {
            if (isUniversalBuffer) {
                throw new UnsupportedOperationException("Cannot create MessageBuffer from a DirectBuffer on this platform");
            }
            // Direct buffer or off-heap memory
            this.base = null;
            this.address = DirectBufferAccess.getAddress(bb) + bb.position();
            this.size = bb.remaining();
            this.reference = bb;
        }
        else if (bb.hasArray()) {
            this.base = bb.array();
            this.address = ARRAY_BYTE_BASE_OFFSET + bb.arrayOffset() + bb.position();
            this.size = bb.remaining();
            this.reference = null;
        }
        else {
            throw new IllegalArgumentException("Only the array-backed ByteBuffer or DirectBuffer is supported");
        }
    }

    protected MessageBuffer(Object base, long address, int length)
    {
        this.base = base;
        this.address = address;
        this.size = length;
        this.reference = null;
    }

    /**
     * Gets the size of the buffer.
     *
     * MessageBuffer doesn't have limit unlike ByteBuffer. Instead, you can use {@link #slice(int, int)} to get a
     * part of the buffer.
     *
     * @return number of bytes
     */
    public int size()
    {
        return size;
    }

    public MessageBuffer slice(int offset, int length)
    {
        // TODO ensure deleting this slice does not collapse this MessageBuffer
        if (offset == 0 && length == size()) {
            return this;
        }
        else {
            checkArgument(offset + length <= size());
            return new MessageBuffer(base, address + offset, length);
        }
    }

    public byte getByte(int index)
    {
        return unsafe.getByte(base, address + index);
    }

    public boolean getBoolean(int index)
    {
        return unsafe.getBoolean(base, address + index);
    }

    public short getShort(int index)
    {
        short v = unsafe.getShort(base, address + index);
        return Short.reverseBytes(v);
    }

    /**
     * Read a big-endian int value at the specified index
     *
     * @param index
     * @return
     */
    public int getInt(int index)
    {
        // Reading little-endian value
        int i = unsafe.getInt(base, address + index);
        // Reversing the endian
        return Integer.reverseBytes(i);
    }

    public float getFloat(int index)
    {
        return Float.intBitsToFloat(getInt(index));
    }

    public long getLong(int index)
    {
        long l = unsafe.getLong(base, address + index);
        return Long.reverseBytes(l);
    }

    public double getDouble(int index)
    {
        return Double.longBitsToDouble(getLong(index));
    }

    public void getBytes(int index, byte[] dst, int dstOffset, int length)
    {
        unsafe.copyMemory(base, address + index, dst, ARRAY_BYTE_BASE_OFFSET + dstOffset, length);
    }

    public void getBytes(int index, int len, ByteBuffer dst)
    {
        if (dst.remaining() < len) {
            throw new BufferOverflowException();
        }
        ByteBuffer src = sliceAsByteBuffer(index, len);
        dst.put(src);
    }

    public void putByte(int index, byte v)
    {
        unsafe.putByte(base, address + index, v);
    }

    public void putBoolean(int index, boolean v)
    {
        unsafe.putBoolean(base, address + index, v);
    }

    public void putShort(int index, short v)
    {
        v = Short.reverseBytes(v);
        unsafe.putShort(base, address + index, v);
    }

    /**
     * Write a big-endian integer value to the memory
     *
     * @param index
     * @param v
     */
    public void putInt(int index, int v)
    {
        // Reversing the endian
        v = Integer.reverseBytes(v);
        unsafe.putInt(base, address + index, v);
    }

    public void putFloat(int index, float v)
    {
        putInt(index, Float.floatToRawIntBits(v));
    }

    public void putLong(int index, long l)
    {
        // Reversing the endian
        l = Long.reverseBytes(l);
        unsafe.putLong(base, address + index, l);
    }

    public void putDouble(int index, double v)
    {
        putLong(index, Double.doubleToRawLongBits(v));
    }

    public void putBytes(int index, byte[] src, int srcOffset, int length)
    {
        unsafe.copyMemory(src, ARRAY_BYTE_BASE_OFFSET + srcOffset, base, address + index, length);
    }

    public void putByteBuffer(int index, ByteBuffer src, int len)
    {
        assert (len <= src.remaining());
        assert (!isUniversalBuffer);

        if (src.isDirect()) {
            unsafe.copyMemory(null, DirectBufferAccess.getAddress(src) + src.position(), base, address + index, len);
            src.position(src.position() + len);
        }
        else if (src.hasArray()) {
            byte[] srcArray = src.array();
            unsafe.copyMemory(srcArray, ARRAY_BYTE_BASE_OFFSET + src.position(), base, address + index, len);
            src.position(src.position() + len);
        }
        else {
            if (hasArray()) {
                src.get((byte[]) base, index, len);
            }
            else {
                for (int i = 0; i < len; ++i) {
                    unsafe.putByte(base, address + index, src.get());
                }
            }
        }
    }

    public void putMessageBuffer(int index, MessageBuffer src, int srcOffset, int len)
    {
        unsafe.copyMemory(src.base, src.address + srcOffset, base, address + index, len);
    }

    /**
     * Create a ByteBuffer view of the range [index, index+length) of this memory
     *
     * @param index
     * @param length
     * @return
     */
    public ByteBuffer sliceAsByteBuffer(int index, int length)
    {
        if (hasArray()) {
            return ByteBuffer.wrap((byte[]) base, (int) ((address - ARRAY_BYTE_BASE_OFFSET) + index), length);
        }
        else {
            assert (!isUniversalBuffer);
            return DirectBufferAccess.newByteBuffer(address, index, length, reference);
        }
    }

    /**
     * Get a ByteBuffer view of this buffer
     *
     * @return
     */
    public ByteBuffer sliceAsByteBuffer()
    {
        return sliceAsByteBuffer(0, size());
    }

    public boolean hasArray()
    {
        return base != null;
    }

    /**
     * Get a copy of this buffer
     *
     * @return
     */
    public byte[] toByteArray()
    {
        byte[] b = new byte[size()];
        unsafe.copyMemory(base, address, b, ARRAY_BYTE_BASE_OFFSET, size());
        return b;
    }

    public byte[] array()
    {
        return (byte[]) base;
    }

    public int arrayOffset()
    {
        return (int) address - ARRAY_BYTE_BASE_OFFSET;
    }

    /**
     * Copy this buffer contents to another MessageBuffer
     *
     * @param index
     * @param dst
     * @param offset
     * @param length
     */
    public void copyTo(int index, MessageBuffer dst, int offset, int length)
    {
        unsafe.copyMemory(base, address + index, dst.base, dst.address + offset, length);
    }

    public String toHexString(int offset, int length)
    {
        StringBuilder s = new StringBuilder();
        for (int i = offset; i < length; ++i) {
            if (i != offset) {
                s.append(" ");
            }
            s.append(String.format("%02x", getByte(i)));
        }
        return s.toString();
    }
}
